The invention relates to an electrical lead configuration especially adapted for use with an electrically heatable fluid heater, such as an electrically heatable catalytic converter, to carry electric current through a surrounding metallic housing to an electrically heatable catalytic converter core, without shorting to the housing.
Catalytic converters are utilized in the exhaust system of internal combustion engines to convert pollutant materials, such as carbon monoxide, unburned hydrocarbons and nitrogen oxides to non-pollutant materials such as carbon dioxide, nitrogen and water. However, in order to be effective at a high conversion rate, the catalyst surface of the converter must be at an elevated temperature in order to convert the exhaust gases to harmless by-products. Hence, it can be useful to initially heat the catalyst prior to engine start-up and during cold starts. To achieve initial heating of the catalyst, one current approach is to provide an electrically heatable catalytic converter, formed usually of a metallic honeycomb heater body which is sealed into the exhaust system, and which is provided with electrical power from the automobile's battery or alternator.
The resistance of the metallic honeycomb heater body is used to heat the converter, and accordingly electric power must be supplied to the heater body at opposite portions thereof. To accomplish this, at least one electrical lead must extend through the housing and be electrically isolated from the housing. Where only one electrode is used, the housing, being attached to the chassis of the automobile, becomes the opposite pole of a voltage source. Where two electrical leads of opposite charge are used, both must extend, in an electrically isolated manner, through the housing and be attached to the metallic heater body.
The most thermally demanding conditions upon electrical leads, such as insulated terminals or electrodes of the prior art, are during the engine operation, when the gas passing through the electrically heated catalytic converter may be at a temperature of between 800.degree. and 1000.degree. C. Some of this heat is transmitted to the electric feed through, such as shown in U.S. Pat. Nos. 5,053,603 to Wagner et al. and 5,238,650 to Sheller et al., resulting in the terminal or connecting electrode being too hot for the convention wire materials and insulation utilized in flexible insulated copper wire to be connected thereto. That is, the conventional insulation utilized in flexible insulated copper wire is usually polyvinyl chloride (PVC) or tetrafluoroethylene resins which have a tendency to melt or dry out and crack under such thermal conditions, resulting in a break down of the insulation. The copper wire then has a tendency to become corroded, due to salt and moisture in the external environment, thus resulting in the failure of an electrical connection to the electrically heated catalytic converter. Further, many terminals of the prior art also suffered problems from gas leakage and corrosion.
It thus has been an object of the invention to provide an improved electrical connection to the metallic heater body of a fluid heater such as an electrically heated catalytic converter, without the detrimental effects and disadvantages encountered with the connecting terminals and electrodes of the prior art.